Initial n_clicks for a Button is None instead of 0 inside a callback

[Akronix]

I have a Button imported from dash_html_components and I'm using it as an Input for a callback. In the very first execution, the initial value of n_clicks is None, but I would expect it to be 0 😕

[chriddyp]

Yeah, that's definitely confusing. Right now, any unspecified property in a dash component defaults to None (so at least the behaviour is consistent).
You can get around this by explicitly setting the initial property of the component in the layout with e.g.

app.layout = html.Div([
    html.Button(n_clicks=0)
])

[Akronix]

Ok that works.
However, it is specially confusing when you see that the Button react component initial state is 0, whereas that in Dash callback it evaluates to None.

[chriddyp]

Yeah, perhaps in the future we can use the values in the defaultProps as the initial state. That could be done as part of the push described in #150 (comment)